Initial information gathering to increase solar on roof

[Bobbo]

Please excuse me because I know less than nothing about solar.

When I bought my Airstream TT in 2017, I had the dealer add the factory solar package. It included one 80 watt solar panel (brand unknown, whatever Airstream uses), one PVCM25D controller from Atkinson Electronics, and a pair of AGM Group 24 batteries.

I am going to get the dealer to increase the solar. I am either going to:

1. add 2 more 80 watt panels in parallel. I know this will work because the controller says it will handle 25 amps, and the 3 panels will be less than that.

OR

2. add 1 more panel wired in series with the current panel, and add 2 more panels wired together in series, then wired in parallel with the first pair. This will double the voltage to the controller, while reducing the amperage to less than option 1 above.

Further information - it would be very difficult to replace the 10g wire from the roof of the TT to the controller. I think (I haven't opened the compartment yet) that it would be easy to replace the 12g wire from the controller to the batteries.

Can this controller handle both of these scenarios?
Is there a significant advantage to replacing the controller?
Is there a better option that I have not considered?

Any and all suggestions are welcome.

[Bobbo]

I am attending the Alumapalooza at the Airstream factory next May. I have an appointment, the week before, at the factory for them to change my single panel to 4 panels, upgrade to an MPPT controller, and add a disconnect switch between the panels and the controller. This will be my last season with a single panel. (I don't trust my local dealer to do this right.)

[Bobbo]

pianotuna wrote:
Hi Bobbo,

I would eliminate the fuse between the panels and the controller and replace it with the Blue Sea.

I would use a temperature sensor on the battery bank to adjust charging voltage for the climate.

Yesterday at -18 c (-2 f), my charging voltage was 15.2

Noted, and added to my list.

[red31]

zenith 40 specs, Max. photovoltaic system input power 550W/12V.
http://www.grapesolar.com/docs/Grape%20Solar%20Zenith%20Series%20Charge%20Controller%20Manual.pdf

normally they use 13v for the calculated limit (13v X 40A) or 520w, the 20A max is 260w, may be a typo! 520w is greater than 480w, unlikely clipping would ever happen!

[pianotuna]

Hi Bobbo,

I would eliminate the fuse between the panels and the controller and replace it with the Blue Sea.

I would use a temperature sensor on the battery bank to adjust charging voltage for the climate.

Yesterday at -18 c (-2 f), my charging voltage was 15.2

[Bobbo]

Let me be sure I have this in my mind correctly. If so, this will be my plan.
1. Change fuse on 10g wire from panels to controller from 10 amp to 30 amp.
2. Replace 12g wire from controller to batteries with 8g wire fused at 50 amps.
3. Install Grape Zenith 40 amp MPPT controller.
4. Install (in parallel) 2 sets of three of the 80 watt panels wired in series.
5. Put a disconnect switch on the hot wire between the panels and the controller. (I have a spare Blue Sea 300 amp disconnect switch laying around.)

Did I miss anything, or get anything wrong?

After getting this set up, I will be back to ask what the optimal settings are that I will need to program.

red31 wrote:
the mppt versions have current-limiting / 'clipping'. 320w in the summer could yield ~20A

from the zennith manual
? A protection feature called current-limiting mode or "clipping" is activated whenever an oversized solar array is producing power which exceeds the controller's rated output.

Let me be sure that I understand this statement. The controller's rated output is 40 amps and the batteries are 12v, so the rated output is 480 watts. Since 6 of the 80 watt panels is theoretically 480 watts, the clipping should not be an issue, right?

[pianotuna]

Not if the panels are wired in series, as input voltage would be approximately 96 volts. #10 can do 30 amps. Thicker from controller to battery bank is a good plan.

There does need to be a disconnect switch, rated for direct current, between the panels and the controller.

Since AGM does want a "wake up" charge at high amperage, more wattage may be desirable, or at least a way to charge each battery individually to keep them "happy".

stacaz822 wrote:
For that many amps coming from the solar panels, you will need at least 4 gauge wire or larger, or you will be losing a lot of power due to heat dissipation. Make sure the solar charger has a four-stage "smart" converter to charge the batteries. If you only have 2 12V AGMs, then a couple hundred watts is certainly enough, unless you run your TV and heater all night...and all day...

[red31]

The 100v limit is based on Voc estimated ~22v, 4 in series would be the limit.
5 x 22v = 110v.
Both the zenith and rover can be adjusted. I believe you need the BT module to adjust eq & abs time. The comet should be able to adjust with the app.
the mppt versions have current-limiting / 'clipping'. 320w in the summer could yield ~20A

from the zennith manual
? A protection feature called current-limiting mode or "clipping" is activated whenever an oversized solar array is producing power which exceeds the controller's rated output.

&



adjustment can be made in "USE" (user) battery type.

[Bobbo]

Then option 3 sounds like the most cost effective solution,but maybe with the COMET 12/24-Volt 40 Amp Solar Charge Controller instead of the Renogy. Three of those panels in parallel gives me 240 watts. Even when I have to replace the batteries, I will never have more than 225AH.

Or, if I stay with option 4 with a Grape Zenith 40 amp MPPT controller, instead of having 3 pairs of solar panels wired in series, I go with 2 sets of 3 solar panels wired in series, or even wire all 6 panels in series? That controller spec sheet says the panel array can go up to 100v. That will cut down on the amps going through the wires.

[stacaz822]

For that many amps coming from the solar panels, you will need at least 4 gauge wire or larger, or you will be losing a lot of power due to heat dissipation. Make sure the solar charger has a four-stage "smart" converter to charge the batteries. If you only have 2 12V AGMs, then a couple hundred watts is certainly enough, unless you run your TV and heater all night...and all day...

[Bobbo]

OK, 1 and 2 are out.

I will probably go with 4 because of the possibility of future growth if necessary. (I won't start with 6 panels. I will start with 4 and evaluate.)

The reason that I am looking at Renogy is that Airstream has run an RJ45 (ethernet) cable from the controller to the wall above the kitchen sink and placed a remote display there. I would really like to use that RJ45 cable to have a remote in that location so I can monitor/adjust the controller without having to disassemble the bed. Also, if that is unused, I have either a hole in the wall, or an ugly, inoperative plate there.

The Renogy does have a temperature sensor if I can figure a way to get it from the underbed area to the battery area on the tongue.

The Renogy does not allow you to adjust the voltage set points.

I am open to other brands. I will look at the Grape.

[pianotuna]

Ty red31,

In that case, I'd buy the Grape MPPT with sensor. I suspect it would be cheaper than the Renogy version.

[red31]

Renogy Rover has remote temp sensor but no remote voltage sensor.
Programming can be done and a BT modul can be added to use the 'Grape' solar app or its cousin app (identical except for screen color) called RenogyBT. Same LCD as Grape 40A BT both made by SRNE solar. Rover is Same controller as Grape Zennith
https://www.homedepot.com/b/Grape-Solar/N-5yc1vZ8p9

Grape's replacement/update to the PWM 40A BT is the Comet
https://www.homedepot.com/p/Grape-Solar-COMET-12-24-Volt-40-Amp-Solar-Charge-Controller-GS-PWM-COMET...

[pianotuna]

1 and 2 are unwise.

3 is possible. Does the Renogy have a temperature sensor on the battery bank? Does it allow you to adjust the voltage set points? If either of those is not true--find a different controller.

4 is what I would choose--but I probably would not do the Renogy controller.

[red31]

2 is a bad choice, the controller can not transform the higher voltage from series panels to battery voltage, 1/2 of the potential power would not be used.

1 is a bad choice, On @ 12.7VDC, Off @ 14.2VDC (flooded) is not a good charge profile.

Tray cable should be increased for any configuration.